What’s the degradation rate of our solar panels after 9 years?
Solar energy is all about kWh. Ultimately, this is what matters. If every day, more and more people across the globe invest in solar energy, it’s because they trust in a future where they self-produce the electricity powering the devices that make their life easier. But investing in a PV system is still a bet based on trust. Because one only buys the promise of future kWh. And we explain regularly in this blog that a two decades module lifespan where everything goes well is not a given. You will discover over the years if you made the right choice. So in order to shed some lights on this topic, we would like to share with you the analysis realized on 16 modules installed almost ten years ago.

How do our solar modules perform after 9 years in operation?
Unsurprisingly, customer satisfaction towards their solar panels is explained by two factors. First, they have to keep their physical integrity and thus should not fail because of one or several of their components. Second, while the solar modules are working properly, they have to produce a maximum of kWh.

“In average, our modules degraded by only -3.5% in 9 years”

We recently analyzed 16 modules installed at our factory in Prenzlau in Germany in order to gather knowledge on their behavior. 8 modules are made of monocrystalline cells while the 8 others embark polycrystalline cells. All those modules have been produced in 2008 and randomly picked to be installed in our test field. You will find in the table hereunder a visual comparison where we display the initial STC value, the measured value after 9 years and finally what would be the power guaranteed under our current linear performance guarantee.

There are three main information to extract from these two graphs:
– In average, the power loss of our modules was -3.5% in 9 years. It turns out that mono modules degrade slightly less but the overall behavior is homogenous between modules and technologies.
– The best module has a power loss as low as -1.5%
– The real behavior is much better than predicted by the linear performance guarantee


How to put in perspective the results?
How should we consider those results? Do they only reflect a very specific case or can they be generalized?


To do so, let’s consider the two imperatives assigned to a good solar panel:
– To be free of failure along the expected lifetime
– To deliver as much kWh as possible


Are our modules default free?
The first and foremost imperative for a solar panel is to work properly without any internal defect. As far as this point is concerned, our 16 modules behave well as after 9 years, none of them display any defect that could potentially harm the integrity of the module in the long run and the performance. This is a very important point to underline. We cannot repeat enough that the main purpose of any international certification like the IEC 61215 should not be misinterpreted. The latter is designed by essence to ensure solar modules are not subject to infant mortality, typically in the first 4 to 5 years. Which means that for the remaining 20 years, it is all about the know-how and commitment of the manufacturer towards quality.
Studies released by Dupont or TUV Rheinland showing that 22% to 48% of modules are having defect after only 4 to 5 years in operation should ring a bell to anyone in our industry. There is such a price pressure and a complexity in the supply chain of components and OEM modules that the quality necessary suffers. It is a proof, if needed, that the price should not be the sole obsession in the PV industry.


Do our modules deliver as much kWh as they should?
The different independent studies that tackled the question of solar modules degradation end up with an average of -0.8% per year. With an average of -3.5% after 9 years, the degradation of the 16 modules tested would translate into an annual degradation of less than -0.4%, which would position aleo in the very good performers among its peers.


All in all, the results shown by this test are consistent with the feedback from our customers and our very low claim rate which makes us confident about our ability to deliver consistently a high level of product quality.


Can past performances predict the future?
One might say that the modules produced in 2008 have barely anything in common with those manufactured in 2017. And it would be right. Almost everything changed. One can also assume that the components used today should be of better quality than those of 10 years ago. Unfortunately, this is not as straightforward as illustrated by field studies cited earlier. Also, some evolutions present in theory greater risks: thinner and thus more fragile cells, thinner backsheet, anti-PID AR coating…


On the other hand, one thing never changed. Despite the huge pressure on costs, we always stayed true to ourselves and our culture of excellence. No matter what. We are in this business to manufacture products that last. Which makes us confident in our ability to provide the same level of quality today as we did already 10 years ago.


Shedding light on a topic like the degradation of solar panels should prompt PV professional to take away 2 key messages:

Simulation will never trump reality – when simulating PV plants performances, it is easy to fall in the trap that consists in taking the first imperative of a good quality for granted while focusing exclusively on simulated yields differences and price of course. Nevertheless, real world data show us that the most pressing need for an investor is to choose the right module, the one that will last and that all other consideration should come afterwards.


Datasheets do not predict yields – datasheets should be taken for what they are. They give indicative and static information. But real life is dynamic and what matters most is how solar modules are designed. You can discuss differences simulated in the low single digit range while forgetting greater risks factors. If, unlike projects developers, you cannot afford third party suppliers to monitor the delivery from a supplier from material selection up to the delivery on site, it is even more important to rely on the established track record and consistency of your supplier to reduce your level of blindness and risk.


You want to receive our latest news and blog articles in your mailbox?
Subscribe to our newsletter.